FLUENT®: Robust, Reliable, Comprehensive CFD

FLUENT 6.3: Faster & More Flexible Than Ever Before
In FLUENT 6.3, a pressure-based coupled solver joins the existing solver options. This new solver can improve solution efficiency as well as convergence and robustness for many cases. With this solver scheme, the pressure and velocity equations are solved in a fully coupled manner, while the other equations are solved sequentially. It is particularly beneficial for “stiff” problems and for solving problems on unusually skewed and stretched meshes.

In addition to this new solver, the existing solvers have been enhanced to offer improved robustness, accuracy, and efficiency. For example, strong shocks can now be captured more effectively with the density-based solver, and transient simulations can be run more efficiently with the pressure-based solver. Additionally, a new diagnostic case check algorithm can be used to assess case settings and offer recommendations to ensure that commonly accepted best practices are being used. Support for polyhedral meshes is being introduced in FLUENT 6.3. These meshes allow the flexibility of an unstructured mesh to be applied to a complex geometry without the overhead associated with a large tetrahedral mesh. Polyhedral meshes are created using automatic cell agglomeration within FLUENT 6.3 to combine tetrahedral cells into polyhedral ones. This can reduce the overall cell count by a factor of 3 to 5. Alternatively, cell-skewness based agglomeration can be used to convert regions with highly-skewed cells to polyhedra, thereby improving mesh quality. The automatic nature of these mesh agglomeration techniques saves the user time, and since the polyhedral mesh contains as few as 1/5 the number of cells in the original tetrahedral mesh, convergence is faster.

In support of FLUENT’s ongoing commitment to parallel processing, numerous improvements to parallel efficiency and flexibility have been implemented along with speed improvements for reading and writing case and data files. HPC customers can also benefit from running Fluent 6.3 on 64-bit Windows platforms such as Windows Compute Cluster Server 2003.


Heat Transfer, Phase Change & Radiation
Several enhancements in FLUENT 6.3 increase the calculation efficiency and range of applicability of the surface-to-surface radiation model. Extensions to the existing model allow the surface-to-surface radiation model to be used for 2D-axisymmetric cases and in cases with multiple cell zones in an enclosure.

For the discrete ordinates radiation model, FLUENT 6.3 provides an option to solve the discrete ordinates and energy equations simultaneously, in a coupled manner. This option helps speed-up cases with extremely high optical thicknesses (>10) for both the gray and non-gray models.

Also new in FLUENT 6.3 is the ability to model multiple species in a real gas- this allows more realistic gaseous mixtures to be simulated than in prior versions of FLUENT.


Dynamic & Moving Mesh FLUENT’s industry-leading dynamic mesh capability for modeling moving objects, such as pistons and valves in IC engines, store separation, and impellers in baffled mixing tanks has been enhanced in FLUENT 6.3. Dynamic mesh techniques can now be applied to a series of related steady-state simulations, easing user set-up. For example, a control valve can be simulated with a range of open positions by building only one mesh and having FLUENT rebuild the mesh for each new position. Other improvements make problem set-up and user-defined mesh motion even more straightforward and efficient.

FLUENT 6.3 is also able to model more complex object motion when using sliding mesh by allowing for multiple sliding mesh regions on one side of an interface to be paired with multiple sliding regions on the opposite side.


Reacting Flow
In FLUENT 6.3, reacting flow simulations benefit from new slow chemistry and micromixing models, useful for liquid reactions and certain combustion applications. Additionally, a larger number of chemical species and reactions can be handled in the non-premixed and partially premixed combustion models. Emissions modeling is more comprehensive through the addition of models for predicting SOx formation and the selective non-catalytic reduction of NOx through urea injection. Expanded in-cylinder combustion capabilities include the ability to model ignition delay in stratified engines, laminar flame speeds for gasoline and a new diesel material.


Turbulence & Acoustics
FLUENT 6.3 continues to enhance its array of turbulence models. When using the DES model, a hybrid of LES and Reynolds-Averaged Navier-Stokes (RANS), the realizable k-epsilon or SST k-omega two-equation RANS models may now be used, expanding the range of applications for which DES is appropriate. Additionally, the time statistics for LES have been extended to include additional unsteady statistics and unsteady wall statistics allowing more information to be gathered from these simulations. Improvements to the RSM Model for low Reynolds number simulations allow turbulent flows that require fine near-wall resolution to be more accurately computed. Also in FLUENT 6.3, users may define their own law-of-the-wall when using k-epsilon turbulence models through the use of user-defined wall functions.


Multiphase
Multiphase modeling continues to be an area of focus for FLUENT 6 development. FLUENT 6.3 provides improved accuracy for transient multiphase simulations. In addition, the Eulerian, mixture and VOF models are now compatible with shell conduction.

Enhancements extend the regimes to which the Eulerian multiphase model can be applied. Both compressible gas and liquid phases can be present, and the mixing plane model is now supported- simplifying the solution of multiphase flows in pumps. Additionally, several options have been added to FLUENT 6.3 for modeling slow granular flows including options for frictional pressure and new options for frictional viscosity.

For free surface flows simulated using the VOF model, a new interface tracking scheme, CICSAM, is available. CICSAM improves solution stability and parallel load balancing and is particularly useful when the viscosity ratio between the phases is high. FLUENT 6.3 also allows a user-defined function (UDF) to be used to specify the wall contact angle, allowing a dynamic value to be calculated from the local flow field. This feature is of primary importance for capillary-driven flows where surface tension is important.

For the discrete phase model, FLUENT 6.3 adds support for the vaporization of multicomponent particles and droplets, including films, and is able to handle the interaction between multicomponent droplets and the continuous phase. This functionality allows fuel vaporization to be modeled more realistically. In addition, particles can be injected from moving boundary surfaces when using the dynamic mesh model and surface normals can be used for the injection direction.


Postprocessing
In FLUENT 6.3, a number of new reporting tools are available for gathering information from FLUENT simulations. These tools include new reports and report options, new time statistics for LES, and new options for injecting flow visualization particles into your domain.

Another improvement in FLUENT 6.3 is the ability to work with third party CAE packages. It is now easier to import and export files to and from other analysis tools (for fluid-structure interaction, for example) and postprocessing tools. Data from cases using from polyhedral meshes can be exported to both Fieldview and EnSight for post-processing and particles and pathlines computed in FLUENT can be exported to EnSight, using EnSight’s format. Additionally, Tecplot export is now supported in the parallel version of FLUENT, streamlining the process for exporting solutions to Tecplot from parallel.


Customized Tools
FLUENT 6.3 expands the flexibility of user-defined scalars by allowing solution in solids zones. User-defined scalars are solved only in the specific fluid or solid zones that are indicated. The non-isotropic diffusivity of user-defined scalar quantities can also be modeled. For user-defined functions, several new or improved hooks are available, including an execute-at-exit hook, and the ability for multiple UDFs to be called at the same point within the FLUENT solution sequence.

Several enhancements have also been made to FLUENT’s add-on modules. A population balance module is new with FLUENT 6.3. This module makes it possible to model multiphase flows with a particle or droplet size distribution. Three approaches are available that account for break-up and agglomeration, so that applications such as bubble columns and crystallizers can be modeled. The proton-exchange membrane (PEM) and solid-oxide fuel cell (SOFC) modules have also been enhanced in FLUENT 6.3. For PEM fuel cells, transient simulations can now be performed and electrical conductivity can be obtained from the FLUENT materials database. For the SOFC module, the range of conditions that can be simulated has been increased.